Specifically, a camshaft system for aircraft engines configured to provide a camshaft lubrication system that enhances the transfer of lubricant to camshaft surfaces even when the aircraft is operated in a manner that locates the rotation axis of the hollow camshaft from horizontal. Generally, an enhanced camshaft lubrication system for hollow camshafts rotationally journaled in a plurality of bearings.
Camshaft systems in aircraft engines are difficult to lubricate. Conventional aircraft engine technology utilizes valves that are operationally responsive to rotating cam surfaces on a camshaft rotationally journaled in a plurality of bearings. The complicated movements of the camshaft and valve systems make the journaled surfaces and the cam surfaces of the camshaft subject to wear during engine operation. Especially, contact between the cam lobe surface and the mating lifter face, tappet, rocker arm, or the like can be subject to an extremely high loading. This high load between the contact surfaces makes fluid lubrication of the sliding surfaces difficult requiring the use of high pressure additives to lubricants.
As a result, conventional aircraft camshaft lubrication technology may be insufficient to prevent frictional power loss, or prevent damage to the cam surfaces, such as pitting, spalling, scuffing, or the like, of the slidingly engaged surfaces. The subsequent failure of the camshaft systems in aircraft engines due to a lack of lubrication at critical times in the camshaft operating cycle has been documented. Firewall Forward Technologies Technical Report No. 1, Firewall Forward Technologies 5212 Cessna Drive, Loveland, Colo. 80538, hereby incorporated by reference herein.
Because there is a large commercial demand for enhanced lubrication systems to resolve the problem of insufficient lubrication of camshaft components during such critical times in the camshaft operating cycle, various types of conventional engine and camshaft lubrication systems have been developed. However, even in light of existing commercial demand and the variety of conventional lubrication technologies that have been developed over the years, significant problems remain unresolved in providing camshaft lubrication technology that provides sufficient lubrication to camshaft components during operation of aircraft engines.
As shown by U.S. Pat. No. 4,991,549, hereby incorporated by reference herein, a conventional method of lubricating camshaft surfaces may be by configuring the cylinder head of the engine to provide xe2x80x9cwellsxe2x80x9d or catch areas in which the lubricant can collect. A significant problem with well type technology may be that the lubricant collected in the wells or catch areas is unfiltered lubricant. As such, the wells or catch areas may accumulate particulate or debris from the unfiltered lubricant. The particulate or debris may then be transferred to the cam lobe surfaces resulting in wear or damage to these surfaces. Another significant problem with well or catch area technology may be that the lubricant migrates in response to the orientation of the engine or the acceleration of the aircraft. As such, the amount of lubricant collected in a particular location may vary significantly depending on the engine orientation (pitch, roll, or yaw) or the acceleration of the aircraft. As the lubricant migrates in response to orientation of the engine or acceleration the amount of lubricant available for transfer to the cam lobes, the amount of lubricant actually transferred to the surface of the cam lobes, or the placement of the lubricant with respect to the cam lobe surface may vary during the operation of the engine. An additional problem with well or catch area technology may be that the oil collected in the wells may be hot. As lubricant circulates through an engine during operation the temperature of the lubricant rises. By the time it is collected in a well or catch area, the lubricant may be sufficiently hot that the lubrication properties of the oil are diminished. A further problem with well or catch area lubrication technology may be the lubricant may not collect or transfer properly to the cam lobe surfaces when the lubricant is cold. Because cold lubricants may exhibit high flow resistance, a cold lubricant may not collect readily into wells or catch areas. As such, there may be little lubricant or a reduced amount of lubricant for transfer to the cam lobe surfaces and little or no lubricant may actually be transferred to the cam lobe surfaces when the engine is started cold.
Similarly, as shown by U.S. Pat. Nos. 4,329,949 and 4,343,270, each hereby incorporated by reference herein, a conventional method of lubricating camshaft surfaces may be to configure the cylinder head, the cylinder head cover, or other engine component to collect excess lubricant so that it may drip onto the cam lobe surfaces. As above, the lubricant may be unfiltered and transfer particulate or other debris to the cam lobe surfaces resulting in unnecessary wear to such surfaces, the amount of lubricant available for transfer to the cam lobe surfaces or the amount actually transferred to the cam lobe surfaces may vary depending on the migration of the lubrication in response to orientation of the engine or the acceleration of the aircraft, the lubricant may have been preheated to a high temperature prior to being dripped onto the cam lobe surfaces, or the lubricant may fail to collect or drip onto the cam lobe surfaces properly when cold.
Another conventional method of lubricating camshaft surfaces may be to spray lubricant onto the camshaft surfaces as disclosed by U.S. Pat. Nos. 6,173,689; 3,628,513; 3,958,541; and 4,343,270, each hereby incorporated by reference herein. In addition to the significant problems discussed above, a further significant problem with spraying lubricant onto camshaft surfaces can be that it results in high oil consumption. As lubricant is sprayed a portion of the lubricant can remain in suspension or mist for a sufficiently long duration and in amounts that may overwhelm the lubricant separator system. The lubricant would then be driven from the engine through the crankcase breather system. Another significant problem with spraying lubricant may be low lubricant pressure or the necessity of increasing the capacity of the lubricant pump. In aircraft, size and weight restrictions may make additional or larger components impractical or impossible to incorporate. Moreover, aircraft engine design and safety specifications are regulated by the federal law which may prohibit the use of spray type technology in aircraft. For example, the usable oil tank capacity may not be less than the product of the endurance of the airplane under critical operation conditions and the maximum oil consumption of the engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling. 14 C.F.R. xc2xa723.1011(c), hereby incorporated by reference herein.
Another conventional method of lubricating camshaft surfaces may be to supply lubricant to the hollow interior of the camshaft and then subsequently deliver the lubricant to the exterior surface of the camshaft as disclosed by U.S. Pat. Nos. 5,450,665; 4,615,310; and Japanese Abstract No 5503755A, each hereby incorporated by reference herein. A significant problem with utilizing the interior of hollow camshafts to deliver lubricant to the cam lobe surfaces may be that lubricant supplied to the interior of the hollow camshaft is not uniformly distributed over the interior surface of the hollow camshaft. As disclosed by Japanese Abstract No. 5503755A, a single feed hole at the drive end of a camshaft (or a single feed hole to the camshaft interior from the drive end bearing) supplies the lubricant to the interior of the camshaft to be distributed to all the cam lobe surfaces and all the camshaft bearings. When lubricant is supplied to the interior of a hollow camshaft through a single feed hole it can take a duration of time for a layer of lubricant to form over the entire interior surface of the camshaft (or may not form at all as to some surface area) after the engine is started. As a result, lubricant supply ducts distal from the single feed may not deliver lubricant to the cam surfaces during engine operation. As such, various attempts have been made to reduce the interior volume of hollow camshafts. For example, the filler elements disclosed by U.S. Pat. No. 4,615,310; and Japanese Abstract Nos. 55-132417 and 57-75105, each hereby incorporated by reference. The failure to deliver sufficient lubricant to the interior of the camshaft or the failure to deliver sufficient lubricant to the exterior surfaces of the camshaft during operation may be exacerbated when the rotation axis of the camshaft is not horizontal. For example, when conventional hollow camshaft technology is operated at twenty degrees attitude, lubricant may only be delivered to the portion of the hollow interior of the camshaft proximate to the lubricant feed hole. Because aircraft routinely operate at attitudes (pitch, roll, yaw) which require the camshaft to operate for a duration of time out of the horizontal position (takeoff, landing, ascent, descent, turns, or so forth) conventional camshaft lubrication technology may not provide sufficient lubricant to all the cam lobe surfaces.
Another significant problem with conventional hollow camshaft lubrication technology may be that the feed holes supplying lubricant to the interior of the hollow camshaft and the lubricant delivery ducts to the cam lobe exterior surface do not have the proper angular displacement. The stream of lubricant supplied to the interior of a camshaft under pressure can disturb the lubricant layer or flow of lubricant on the interior surface of the hollow camshaft as shown by FIG. 5. When the lubricant feed hole is located approximately opposite the lubricant delivery hole to the cam lobe surfaces the lubricant entering the interior of the camshaft may disturb the lubricant pooled on the opposite side of the interior surface of the camshaft and prevent or impede lubricant from entering the lubricant delivery hole to the cam lobe surfaces. As such, the cam surface may not be supplied with a sufficient amount of lubricant to prevent damage.
Another significant problem with conventional hollow camshaft lubrication technology may be that lubricant layer or lubricant stream may be insufficient to supply lubricant to multiple lubricant delivery holes. A first lubricant delivery hole may utilize the entire amount of lubricant that flows over it. As such, a second lubricant delivery hole positioned to take advantage of the same portion of the lubricant stream or lubricant flow as the first lubricant delivery hole may not receive an adequate supply of lubricant.
Another significant problem with conventional hollow camshaft lubrication technology may be that modifications to increase the amount of lubricant to the cam lobe surfaces, such as increasing the aperture size, can overtax standard lubricant pressurization pumps. The subsequent reduction in lubricant pressure may result in insufficient delivery of lubricant to the exterior surfaces of the modified camshaft. See, Firewall Forward Technologies Technical Report No. 2, hereby incorporated by reference herein.
Another significant problem with conventional hollow camshaft lubrication technology may be that there is not a vent hole in the hollow camshaft. The absence of a vent hole can prevent or impede moisture or lubricant vapor, gases, or the like, from being transferred from the interior volume of the camshaft. As such, increased pressure in the interior of the hollow camshaft must be transferred from the lubrication supply ducts to the exterior surfaces of the cam lobes. Relieving pressure through these supply ducts may interrupt the continuous flow of lubricant from the lubricant supply duct to the cam lobe surface.
With respect to each of the above-described problems with conventional camshaft lubrication technology, and specifically with respect to the problems with the use of conventional camshaft lubrication technology in the context of aircraft engines, the present invention discloses camshaft lubrication systems that address each in a practical fashion. The invention also satisfies the long felt but unresolved need for a reliable camshaft lubrication system for aircraft engines. Moreover, while the instant description provides numerous examples of the invention in the context of aircraft and aircraft engines, it is understood that the inventions disclosed may be used in a wide variety of applications, including but not limited to, automobile engines, marine engines, motorcycle engines, high performance engines, or the like.
Accordingly, a broad object of embodiments of the invention is to provide a camshaft lubrication system that provides both camshaft apparatuses and camshaft lubrication methods that may be used in aircraft engines, or used in other types of engines such as automobiles, boats, motorcycles, or the like.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and methods of lubricating camshafts that can be used in a wide variety of valve mechanism applications, such as, valve mechanisms that are responsive to tappets, lifters, rocker arms, or the like; or when the camshaft is located overhead cam; or the camshaft employs push rods; or used in conjunction with hydraulic lash adjusters, or the like.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and methods of lubricating camshafts for engines that operate the camshaft at various amounts of pitch, roll, or yaw, such as a pitch of 5 degrees, 10 degrees, 15 degrees, 20 degrees, or more from horizontal.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and camshaft lubrication methods that can replace factory specification camshafts approved for use in airplane engines such as Continental or Lycoming aircraft engines, for example.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and camshaft lubrication methods that provide a sufficient lubrication layer to form on the interior surface of hollow camshafts to provide sufficient lubricant to each cam surface lubrication supply duct.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and camshaft lubrication methods that provide proper angular displacement of the camshaft lubrication supply ducts and the cam surface lubrication supply ducts so that lubricant entering the interior of the camshaft does not disrupt the delivery of lubricant to proximate lubrication supply ducts.
Another broad object of embodiments of the invention can be to provide a camshaft apparatuses and camshaft lubrication methods that provide proper angular displacement of multiple cam surface lubrication supply ducts so that lubricant flow over the first duct does not disrupt or impede the flow of lubricant to the remaining ducts.
Another broad object of embodiments of the invention can be to provide camshaft apparatuses and camshaft lubrication methods that provide proper ventilation of the interior volume of a hollow camshaft.
Another object of embodiments of the invention can be to provide a reduced wear camshaft apparatus.
Naturally further objects of the invention are disclosed throughout other areas of the specification and claims.